There is a general desire to improve the capacity and performance of switches/routers in optical telecommunication systems. One approach is to employ wavelength division multiplexed signals and wavelength selective switches (WSSs), which may be employed in a reconfigurable optical add/drop multiplexer (ROADM) or the like. Background prior art can be found in U.S. Pat. Nos. 7,397,980 8,867,917.
We have previously described techniques for mitigating crosstalk in such devices (our WO2012/123715) but there is a general drive for still further improved performance and, in particular, techniques which can mitigate deleterious effects which can accumulate when multiple switches are cascaded.